The present invention relates to an adjustable safety steering column for a motor vehicle and, more particularly, to a column with a telescopable steering spindle disposed in outer casing parts and supported by a deformation element.
German Patent Document DE-PS 33 18 935 shows an axially adjustable steering column for a motor vehicle in which a toothed rack is connected with an inner casing tube and a pinion of an adjusting motor engages in the toothed rack. As a result, the casing tube part with the connected steering spindle is axially displaced. An energy-absorbing device is not provided in the case of this steering column. Another steering column is shown in German Patent Document DE-AS 16 30 847 and is constructed as a safety steering column with a deformation element between a casing tube and a body-side support. This deformation element deforms in the case of a crash in which case the divided steering spindle telescopes. An axial adjustment of the steering column for the purpose of adapting it to the driver is not possible with this steering column.
It is an object of the present invention to provide an adjustable steering column which complies with the safety requirements in the case of a crash.
This object has been achieved in accordance with the present invention by configuring a first outer casing tube part as a deformation element supported, on an end side, on an inner casing tube surrounding the deformation element. The inner casing tube has a toothed rack into which a pinion of an adjusting device engages for axial displacement of the steering column.
One of the principal advantages achieved by the invention is that a steering column of a compact construction is provided which is axially adjustable and, at the same time, absorbs energy.
In addition to the axial displacement of the steering column, the adjusting device also permits a holding-fast of the deformation element in the case of a crash. Since a direct linking to the vehicle body does not exist, the steering column is supported by way of a pinion of the adjusting device which engages in a toothed rack on the deformation element.
In one embodiment of the present invention a first outer casing tube part, on which the steering spindle is disposed, is integrally connected with the deformation element which corresponds approximately to the outside diameter of the casing tube part. Following the first outer casing tube part, an inner casing tube extends which encloses the deformation element and to which the deformation element is fastened on the end side. This type of connection of the deformation element with the inner casing tube permits, by way of a toothed rack connected with this part and by way of an engaging pinion, the axial displacement of the steering column as well as an arresting of the steering column.
Preferably the inner casing tube is supported with its end facing away from the fastening point to the deformation element on the first outer casing tube part and may be fastened by way of shearable plastic pins. Thus, for the axial displacement, an introduction of force may also take place by way of this connected end and, in the case of a crash, a corresponding coordination takes place for absorbing energy.
The deformation element is guided inside the cylinder of the inner casing tube and on the steering spindle. That is, the deformation element rests against the inner circumferential surface and on the outer surface so that no buckling of the deformation element can take place in the case of a crash as well as in the case of an axial displacement of the steering column.
The deformation element preferably comprises a corrugated tube and is constructed in one piece with the casing tube part in that the end of the casing tube part is upset correspondingly in a special process. Also within the scope of the present invention is a corrugated tube which is separate from the casing tube part as well as corresponding deformation elements which have an energy-absorbing effect.
The steering spindle has a divided construction in the area of the inside casing tube and the parts are displaceably connected with one another by way of longitudinal toothing. Another division of a connecting steering spindle is provided in the area between a steering gear and a joint.